Unable to update Windows XP

A problem on your computer is preventing updates from being downloaded or installed

Click Start > Run and type

regsvr32 wuapi.dll
regsvr32 wuaueng1.dll
regsvr32 wuaueng.dll
regsvr32 wucltui.dll
regsvr32 wups2.dll
regsvr32 wups.dll
regsvr32 wuweb.dll

Reference
http://www.technipages.com/error-a-problem-on-your-computer-is-preventing-updates-from-being-downloaded.html